calphy-alchemy

Run calphy alchemical transformations: mode: alchemy to get the free-energy difference between two interatomic potentials for the same structure (upsampling a cheap potential to an expensive one, comparing potentials), and mode: composition_scaling to get the free-energy change with composition or the cost of substitutional defects. Use when the question is a free-energy difference between two Hamiltonians or two compositions rather than an absolute free energy.